In medical or health procedures, use of guides improves the accuracy of instrument placement into tissue. In addition, imaging systems provide visual guidance based on measurements from various imaging formats. These imaging formats (such as Magnetic Resonance Imaging (MRI), sonographs (ultrasound), fluoroscopy, X-ray, and the like) can locate an interventional device in relation to treatment or therapy-targeted tissue, such as MRI-detected target tissue. These imaging formats can generate imaging data that may be used to determine the appropriate positing of the interventional device or instrument.
As an example, MRI may be used to detect faint nuclear magnetic resonance (NMR) signals limited by protons in the presence of a string magnetic field after excitation by a radio frequency signal, such as by way of antenna(e) termed “coils”. The detected signal can then be analyzed to produce an image of the internal structure of tissue within the patient being imaged.
For purposes of example, when attempting to examine breast tissue, the tissue of interest may be compressed or held in position between two immobilization plates, which may hold the breast in a medial-lateral direction such that it is immobilized during acquisition of an MRI image. These immobilization plates may further consist of a number of apertures, and with a plurality of apertures such that a grid, or other co-ordinate positioning system, can be formed. These apertures may also allow interventional devices to pass through the immobilization plate to access the tissue. Immobilization plates having a large number of apertures in a grid pattern sized to support and guide interventional devices, can tend to be cumbersome as, for example, a new plate may be required for interventional devices having different diameters. This may require the use of a different immobilization plate for each intervention guide being used. This also may prevent the ability to use interventional devices of different diameters without multiple scans. Furthermore, this may cause shifting in the tissue being immobilized when plates are being exchanged or moved. Immobilization plates, therefore, may alternatively have apertures larger than the interventional devices, into which an adaptor, guide, block or plug may be inserted. These can be generically referred to as guide plugs, which may have one or several holes for assisting in positioning an interventional device to a target. The guidance may be provided by, for example, a grid of holes, which may be perpendicular to the immobilization plate, through the plug. Alternatively a plug may be provided with a non-grid pattern of holes, perpendicular to the immobilization plate, in various parts of the plug where the plug may be movable to multiple positions, for example by removing the plug and re-inserting the plug into the immobilization plate in a different orientation, to align one of the holes as close as possible with the target region of the tissue. As a consequence, the positioning capability of any interventional device is limited.